Doppler Constraints on Planetary Companions to Nearby Sun-like Stars: An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions*  

Abstract

Directly imaging temperate rocky planets orbiting nearby, Sun-like stars with a 6 m class IR/O/UV space telescope, recently dubbed the Habitable Worlds Observatory, is a high-priority goal of the Astro2020 Decadal Survey. To prepare for future direct imaging (DI) surveys, the list of potential targets should be thoroughly vetted to maximize efficiency and scientific yield. We present an analysis of archival radial velocity data for southern stars from the NASA/NSF Extreme Precision Radial Velocity (EPRV) Working Group’s list of high-priority target stars for future DI missions (drawn from the HabEx, LUVOIR, and Starshade Rendezvous studies). For each star, we constrain the region of companion mass and period parameter space we are already sensitive to based on the observational baseline, sampling, and precision of the archival radial velocity (RV) data. Additionally, for some of the targets, we report new estimates of magnetic activity cycle periods, rotation periods, improved orbital parameters for previously known exoplanets, and new candidate planet signals that require further vetting or observations to confirm. Our results show that for many of these stars we are not yet sensitive to even Saturn-mass planets in the habitable zone, let alone smaller planets, highlighting the need for future EPRV vetting efforts before the launch of a DI mission. We present evidence that the candidate temperate super-Earth exoplanet HD 85512b is most likely due to the star’s rotation, and report an RV acceleration for δ Pav that supports the existence of a distant giant planet previously inferred from astrometry.

Setting the Stage for the Search for Life with the Habitable Worlds Observatory: Properties of 164 Promising Planet-survey Targets

“…Additionally, future work should include determining the depth of past searches for planets in these systems using archival photometry and public RV observations (e.g., Howard & Fulton 2016;Laliotis et al 2023). A follow-up investigation of stellar variability and rotation rates would also be useful for accurately measuring stellar ages with gyrochronology, and as a proxy for stellar activity.…”

Closeby Habitable Exoplanet Survey (CHES). I. Astrometric Noise and Planetary Detection Efficiency Due to Stellar Spots and Faculae

“…With the development of the new generation of extreme-precision spectrographs, the RV measurement at sub-meter-per-second precision becomes feasible, including the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO; Pepe et al 2010), the EXtreme PREcision Spectrograph (EXPRES; Jurgenson et al 2016), and NEID (Lin et al 2022). The previous investigations showed that the amplitude of RV variations resulting from stellar activity ranges in the order of a few meters per second (Hatzes 2002;Butler et al 2006Butler et al , 2017Lagrange et al 2010;Laliotis et al 2023). The dispersion in RV due to granulation is estimated to be larger than 0.3 m s −1 , significantly surpassing the signals emanating from terrestrial planets (approximately ∼0.09 m s −1 ).…”

The Death of Vulcan: NEID Reveals That the Planet Candidate Orbiting HD 26965 Is Stellar Activity*

“…Most recently, Laliotis et al (2023) returned to the target as part of a larger survey of Sun-like stars with host planets for potential direct imaging. They also argue that the signal is likely activity, as they find a significant Hα signal at a period of about 43.5 days, very close to the proposed Ma et al (2018) signal though not quite at the 42-day period, further placing the planet hypothesis into question.…”